This invention is related, in a broad sense, to a hydraulic piston apparatus and particularly to a hydraulic pump and a hydraulic motor as a hydraulic piston apparatus.
More specifically, it relates, in its third and seventh embodiments, to a variable capacity hydraulic piston apparatus of a variable capacity type which is simple in structure and has a long service life.
The "piston" used herein is of the type for feeding and receiving a hydraulic pressure within a cylinder and in which its length (whether it is long or not) with respect to its diameter is not significant.
As for hydraulic pumps and motors, many proposals have heretofore been made. Some of the representative examples of such proposals are gear pumps, vane pumps, piston pumps, axial piston pumps and the like. As for variable capacity pumps among them, cam plate type piston pumps occupy a prominent position among pumps of the type which have a comparatively high discharge pressure as shown in FIG. 3.
The reason is that employment of pistons (plungers) 1, 1a make it easy to obtain a liquid confined pressure within cylinder chamber 2, 2a and the discharge quantity can be optionally established by changing the angle of a cam plate 3. Another reason is that management of accuracy of the outer diameters of the cylindrical pistons 1, 1a and the inner diameter of the cylinder is easy and manufacturing cost can also be reduced.
On the other hand, as is shown in FIG. 3, a linkage between the cam plate 3 and piston rods 4, 4a, and a service life of a connecting portion between an input rotational shaft 5 and the cam plate 3 have heretofore been considered to involve problems. Regarding the single body of the piston, current flow becomes an alternating flow owing to reciprocating motion. A method for sealing a current plate for converting the alternating current to an unidirectional direct current also becomes a big problem.
The axial pump cannot escape from this problem as long as it has the same construction.